Comparison of video camera sled with diver surveys for Puerto Rico queen conch (Lobatus gigas)

Queen conch Lobatus gigas is one the most important fisheries species in the Caribbean with annual landings worth > US$30 million, but are overfished in most parts of the Caribbean. Abundance surveys have been conducted in Puerto Rico by scuba divers 5-year intervals, but have not been completed in recent years due to availability of funding and trained divers. Diver surveys are also limited by depth and time. In contrast, underwater video or camera surveys are not constrained by these factors and also provide a permanent photo record of observations. We conducted a survey of queen conch density on the western shelf of Puerto Rico in 2016 using two different methods: divers and a camera sled. Divers surveyed eight transects of 2-3 km using diver propulsion vehicles and historical methods. The camera sled was fitted with a digital camera, synchronized strobe lights, and paired lasers, and was towed along the dive transects several days later. Conch densities (#conch/ha) estimated with the camera sled were significantly higher than those estimated by diver survey methods. Additionally, conch measurements estimated using paired lasers were smaller than diver estimates, but more accurate. These results may lead to further applications or development of sled survey techniques, and improved data collection and analysis that can be used for management of queen conch in the Caribbean. This project was funded by the NOAA Saltonstall-Kennedy Program. Our sled was designed by Mark Blakeslee, and camera equipment was built by Scott McEntyre.

Below: PhD Student Wilmelie Cruz-Marrero with the digital camera sled.